Interpupillary distance measuring device

ABSTRACT

An instrument for measuring the interpupillary distance of a subject is described which comprises two parallel sighting tubes disposed in adjustable spaced relationship along parallel optical axes and interconnected for measuring the spacing between the axes, two eyepiece lenses of preselected equal focal length disposed at corresponding first ends of the sighting tubes, first and second translucent targets bearing recognizable indicia disposed along respective sighting tubes a distance from the lenses equal to the focal length, and an aperture near each lens for limiting the size of the field of view along each optical axis.

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured and used by or forthe Government of the United States for all governmental purposeswithout the payment of any royalty.

BACKGROUND OF THE INVENTION

The present invention relates generally to clinical instruments for theexamination of eyes, and more particularly to a portable instrument formeasurement of the interpupillary distance.

Interpupillary distance measurements are made by opticians, optometristsand ophthalmologists for clinical purposes, prescriptions foreyeglasses, and similar and related purposes. Previously availabledevices for measurement of interpupillary distances may be exemplifiedby those described by or referenced in U.S. Pat. Nos. 2,361,534 and4,244,639. Existing devices normally require a separate operator tofocus and/or align the optics thereof, to make measurements and tointerpret results.

The invention provides a simple, cost effective, accurate and reliablesubject operated instrument for measurement of the interpupillarydistance. The invention presents recognizable optical images torespective eyes of a subject sighting along the optical axes of a pairof parallel sighting tubes. The tubes are movable with respect to eachother and are interconnected by a scale for displaying the spacingbetween the optical axes. The subject adjusts the separation of thetubes until the images appear superimposed and reads the interpupillarydistance from the scale.

It is, therefore, a principal object of the invention to provide animproved eye examinaton instrument.

It is another object of the invention to provide a subject operatedinstrument for measurement of the interpupillary distance.

These and other objects of the invention will become apparent as thedetailed description of representative embodiments proceeds.

SUMMARY OF THE INVENTION

In accordance with the foregoing principles and objects of theinvention, an instrument for measuring the interpupillary distance of asubject is described which comprises two parallel sighting tubesdisposed in adjustable spaced relationship along parallel optical axesand interconnected for measuring the spacing between the axes, twoeyepiece lenses of preselected equal focal length disposed atcorresponding first ends of the sighting tubes, first and secondtranslucent targets bearing recognizable indicia disposed alongrespective sighting tubes a distance from the lenses equal to the focallength, and an aperture near each lens for limiting the size of thefield of view along each optical axis.

DESCRIPTION OF THE DRAWINGS

The invention will be clearly understood from the following detaileddescription of representative embodiments thereof read in conjunctionwith the accompanying drawings wherein:

FIG. 1 is a schematic in partial cutaway of a binocular interpupillarydistance measuring instrument of the invention;

FIG 1a is a view of the instrument of FIG. 1 along line A--A;

FIG 1b is a view of the instrument of FIG. 1 along line B--B; and

FIG. 2 is a superposition of images as viewed by a subject in the use ofthe instrument of FIG. 1.

DETAILED DESCRIPTION

Referring now to the drawings, shown in FIG. 1 is a schematic in partialcutaway of binocular interpupillary distance measuring instrument 10 ofthe invention. Instrument 10 comprises two sighting tubes 11,13 disposedalong parallel optical axes L,R for viewing by respective left and righteyes of subject S. Tubes 11,13 are connected to corresponding elementsof a movable indicator 15 and scale 17 which hold tubes 11,13 inadjustable parallel spaced relationship. Scale 17 is calibrated toprovide a direct reading of the spacing between axes L,R (interpupillarydistance). At respective first ends 19,21 of tubes 11,13 are mountedeyepiece lenses 23,25 having equal preselected focal length f. Apertures27,29 disposed near respective lenses 23,25 limit to preselected sizethe available solid viewing angle along axes L,R. Second ends 31,33 oftubes 11,13 include translucent light diffusing disks 35,37 fordiffusing ambient light 38 admitted into tubes 11,13 along axes L,R.Targets 39,41 are disposed along tubes 11,13 a distance equal to focallength f from lenses 23,25 for simultaneous viewing by respective leftand right eyes of subjects. Targets 39,41 each comprise a recognizableindicia on a translucent disk.

FIGS. 1a,1b are views of instrument 10 along lines A--A and B--B showingrepresentative configurations for respective targets 39,41. Target 39may comprise a circle and cross. while target 41 may comprise twoconcentric circles. Other combinations of targets may be used as wouldoccur to one with skill in the field of the invention, so long as thesuperposition (binocular fusion) of the images as viewed by subject Salong axes L,R is easily identified. Targets 39,41 must be different toensure that subject S does not mistake suppression of one eye for fusionof the targets.

In the use of instrument 10 for measuring the interpupillary distance,subject S views targets 39,41 along respective axes L,R and adjusts thespacing of tubes 11,13 using adjusting screw 43 until targets 39,41appear superimposed as suggested in FIG. 2. The interpupillary distanceis read directly from calibrated scale 17.

The invention therefore provides a novel subject operated instrument formeasurement of the interpupillary distance. It is understood thatmodifications to the invention as described may be made as would occurto one with skill in the field of the invention within the scope of theappended claims. All embodiments contemplated hereunder which accomplishthe objects of the invention have therefore not been shown in completedetail. Other embodiments may be developed without departing from thespirit of the invention or from the scope of the claims.

I claim:
 1. An instrument for measuring the interpupillary distance of asubject, comprising:(a) a first sighting tube and a second sighting tubedisposed in adjustable parallel spaced relationship along respectiveparallel first and second optical axes; (b) means interconnecting saidfirst tube and said second tube for selectively adjusting said firsttube in said adjustable parallel spaced relationship relative to saidsecond tube and for gauging the spacing between said first and secondoptical axes; (c) a first eyepiece lens and a second eyepiece lens,having equal preselected focal lengths, disposed along respective saidfirst and second optical axes at corresponding first ends of said firstsighting tube and said second sighting tube; and (d) a single firsttranslucent target bearing a first recognizable indicia disposed withinsaid first tube along said first optical axis a distance equal to saidpreselected focal length from said first lens, and a single secondtranslucent target bearing a second recognizable indicia different fromsaid first recognizable indicia disposed within said second tube alongsaid second optical axis a distance equal to said preselected focallength from said second lens, said first recognizable indicia and saidsecond recognizable indicia being optically fusible by said subjectsighting along respective said first and said second optical axes in byspacing said first sighting tube and said second sighting tube adistance corresponding to the interpupillary distance of said subject.2. The instrument of claim 1 further comprising first and secondapertures of equal preselected size disposed adjacent respective saidfirst lens and said second lens for limiting the angular field of viewalong each of said first and second optical axes to preselected size. 3.The instrument of claim 1 further comprising means disposed atcorresponding second ends of said first tube and said second tube foradmitting diffuse light into said first tube and said second tube alongrespective said first and second optical axes for diffusely illuminatingsaid first target and said second target.